PROJECT SUMMARY Cellular senescence, one of the major hallmarks of aging, describes the sudden inability for cells to divide. Senescent cells often accumulate with age, in response to physical and chemical stressors (genomic instability, telomere attrition, irradiation, etc.), though the overlap between these stressors and neurological diseases such as Alzheimer?s Disease (AD) is currently unknown. In-vitro experiments of senescence often utilize contrived stressors such as hydrogen peroxide or radiation, that may not be physiologically relevant for age-related diseases such as AD. Furthermore, the senescence phenotypes observed in vitro are likely not complete models for what is occurring in dynamic biological systems. Soluble amyloid-beta oligomers (Abo), an important hallmark in AD, have been shown to potently induce senescence in a variety of brain cell types and environments, in contrast to fibrillar Ab. Abo is thought to bind membrane proteins and subsequently signal downstream aggregation of related amyloids such as tau. In fact, the presence of endogenous Abo is one of the strongest indicators of disease severity in AD models and organisms, suggesting a link between AD and cellular senescence that is only beginning to be explored. In order to study this association, we propose to combine gold-standard techniques and single-cell omics data in order to define heterogenous genetic and epigenetic signatures of senescence that are distinctly a function of their induction type. Doing so will also produce robust signatures and biomarkers of senescence in brain cells that can be utilized for the pathological phenotyping of human tissues. These measures will also allow for the comparison of disparate senescent behaviors to help identify lab-derived amyloids that best resemble patient-derived constructs. We will evaluate multiple lab-derived Abo constructs, including those stabilized from lipids located in predominantly diseased regions of the brain. Observations would be synergistically coupled with solution biophysics experiments and molecular modeling, providing analogous structural data for each inducer type. Taken together, these measurements will uniquely profile senescence in brain cells, define the degree of overlap between endogenous senescence inducers and those reconstituted in the lab, and highlighting how AD risk is modulated by cellular senescence.